Molded electrolytic capacitor



Feb. 10, 1953 H. E. BRAFMAN MOLDED ELECTROLYTIC CAPACITOR Filed July ll, 1950 Fig.

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HAROLD E. BRA/:MAN

H/S TTORNE Patenteci Feb. 10, 1953 UNITED STATES PATENT OFFICE MGLDED 'ELECTROLYTIC 'CAPACITOR Harold E. Brafman, North Adams, Mass., as-

signor to Sprague Electric Company, North Adams, Mass., acorporation of Massachusetts Application July 11, 1950, Serial No. 173,111

lClaims. 1

The present invention relates to electrolytic capacitors and in particular to electrolytic capacitors having molded cas-ings.

Electrolytic capacit rs normally include electrolyte compositions which during use, particularly under lhigh held strengths, may produce gases such as hydrogen. low molecular weight hydrocarbons and the like. Since it is necessary that electrolytic capacitors be more or less sealed in vorder that they lbe stable under various opn erating conditions, there is the ever present danger that "the evolved gases will build up a pressure within 'the sealed sufficient to burst the capacitor housing. In this event there in danger that fragments. of the housing will cause considerable damage. Because of this and for other reasons of safety, electrical underwriters reduire the provision of venting means for all electrolytic capacitorsY operating at high iield strengths.

The provision or a venting Ymeans to meet underwriter requirements increases production problems and results in higher costs for the capacitor. Various :venting means. are `employed on metal can type electrolytic capacitors;

however, each of these means involve special and separato production operations and apparatus that ,are both time consuming and expensive.

It is an object of the present invention to overcome the foregoing and related disadvantages. It is another object to produce a low cost molded electrolytic capacitor. .lt is a further object to produce a vented molded tubular electrolytic capacitor that will meet electrical underwriters standards. rFliese and other objects .of the .invention 'will become apparent from the description and claims that follow.

These objects are attained in accordance with the present invention wherein there is produced a vented molded tubular electrolytic capacitor comprising a convolutely wound electrolytic capacitor section, an electrically conducting terni'inallead connected to one electrode of said section, and an electrically conducting eyelet `connected to the'other electrode of said section and having an opening therein for the impregnation. of the section with electrolyte, a inolded thermosetting'resin casing enclosing said section but leaving the eyelet opening exposed, at least one electrolyteimpervious yields-ble barrier in said casing providing for the safe escape of .gas from said capacitor, the interior of said capacitor being impregnated with electrolyte and said opening in said eyelet being sealed, and an electrically conducting terminal lead being conductively connected to said eyelet. The impervious yieldable barrier is preferably an elastomer such as rub.- ber. The invention may take several forms, for instance the casing may have cavities `or openings lled with the elastomer or a strip of the elastomer may be placed .between the capacitor section and the casing so as to block openings in the casing and form a seal between the casing and the capacitor section. Under certain circumstances tfze elastomer may be in the form of `a washer or an end cap sealing the casing to a 'ter'- minal. lead the capacitor. It is further contemplated that the entire capacitor section, eX.,- cept for the eyelet opening, may be encased Vin a sheath of the elastomer compound. In order to malte the latter capacitor more rigid and stable an outer molded resin casing having cavities therein, and as previously described, may enclose the elastomer encased section.

The invention will be more fully described with reference to the appended drawings wherein:

Figures .1, 3, 5 and 8 show in partial cross-sec-v tion several capacitors produced in accordance with various embodiments of the present invention,

Figure 2 is a View taken along the .section 2 2 of Figure 1,

Figure 4 is. a View taken along the section *1 -4.

of Figure 3,

Figure 6 is an end view of the elastomer cap shown in Figure 5,

Figure '7 is a side cross-section view of the cap is shown a vented molded tubular electrolytic` capacitor i@ comprising a convolutely wound electrolytic capacitor section I2, an electrically conducting tinned terminal lead l-i connected to one electrode of section l2 by means of solder l, and electrically conductingeyelet IS hav-- ing an opening 2s therein for the impregnation of electrolyte (not shown) into section i2 connested to the other electrode of section i2 by means of solder 22, a molded thermosetting phenol-formaldehyde resin casing or the like, 24 enclosing section I2 except for opening 213 in eyelet I8, openings 2S, 28 in the casing 24, and an elastomer strip lof rubber or a suitable silicone plastic resin 3d (by silicone it is meant an organo-substituted polysiloxane in which the organo groups are bonded by carbon-to-silicon bonds) engaged between section l2 and casing 24 sealing the openings '25, 28. After impregnation with electrolyte a tinned terminal lead 3B may be inserted in opening Z0 of eyelet I8 and soldered thereto by means of solder 32 which also hermetically seals the capacitor ill.

The embodiment of the invention shown in Figures 3 and 4 is similar to that shown in Figures 1 and 2 except that the elastomer strip 34 is not employed, instead openings 26, 28 are lled with an elastomer plug such as 50, 52.

Figures 5, 6 and 7 show another variation of the present invention. Here there are neither strip 34 nor openings 26, 23. Instead capacitor section l2 is provided with an elastomer end cap 60 formed to t securely over the end of section I0 and having an opening 62 therein through which terminal lead I4 may project.

The embodiment of the invention shown in Figures 8, 9 and 10 is similar to that shown in Figures 5, 6 and 7 except that end cap 62 is replaced by elastomer washer 10. The washer 7B is provided with an annular indentation 72 to securely engage it to capacitor casing 24.

When openings such as 26, 28 are employed to provide the capacitor with venting means, it is desirable that they be at leas e" in width.

In the present invention an electrolytic capacitor section formed in accordance with known procedure such as disclosed in Burnham U. S. P. 2,444,725 issued August 9, 1944, is electrically terminated and encased in a thermosetting resin casing as disclosed in copending application Serial No. 718,962. Knockout pins are usually employed to aid in removing the iinished casing from the mold. In accordance with the present invention the length of at least one of the knockout pins used may be extended above the bottom of the mold to form a cavity or opening in the resin casing. A strip of elastomer may be placed so as to be disposed between the extended knockout pin or pins, and the capacitor section so that perfect sealing between the elastomer, the section, and the casing is effected by the pressure exerted during the molding cycle. If the strip of elastomer is not employed to seal the casing cavities, other means such as have been previously described may be employed to do so. The so encased capacitor may then be impregnated through the eyelet with a suitable electrolyte such as described in the Burnham U. S. P. 2,444,725.

Pre-forms of partially molded phenol-forinaldehyde resin may be used to facilitate the nal molding of the capacitors. This is usually done by preparing similar top and bottom pre-forms approximately corresponding to the longitudinally split Aiinal casing. One pre-form may then be placed in the bottom of a suitable mold carrying knockout pins which penetrate the pre-form, alstrip of elastomer placed over this pre-form, the unimpregnated capacitor section put in place, the section covered with the top pre-form and the upper section of a mold fitted over the entire combination. Heat and pressure are then applied for the required time after which the mold is opened and the semi-iinished capacitor removed as by ejection with the knockout pins. The pre-forms may be made in any convenient shape and can be similarly used with any of the above-described variations. It is also feasible to make the knockout pin or pins of such a length as to leave a thin layer of resin between the capacitor section and the atmosphere. In this event the thin layer will harmlessly give way under the internal stress set up by gas evolution, before the entire casing is subject to any danger of explosion. The thin resin layer can be used either by itself or in combination with an elastomer wall as described above.

Although I have described in particular the use of a heat and pressure molded phenol-formaldehyde casing about the capacitor section, other suitable cast or pressure molded casings may be used. Barrier-exposing openings may be provided in either or both the top and bottom casing pre-forms when pre-forms are used in the molding operation. The capacitor of the invention can also have its casing applied by other molding methods not using pre-forms. Thermosetting casings are preferred over thermoplastic casings because of the improved rigidity; however, thermoplastic resins such as polyethylene, polystyrene, polyvinyl chloride are satisfactory for certain purposes such as condensers operating at relatively low temperatures.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope hereof, it is to be understood that the invention is not limited to the specific embodiments hereof except as defined in the appended claims.

What is claimed is:

1. A vented molded tubular electrolytic capacitor .consisting essentially of a convolutely wound electrolytic capacitor section, an electrically conducting terminal lead connected to one electrode of said section, and an electrically conducting eyelet connected to the other electrode of said section and having an opening therein for the impregnation of electrolyte, a molded thermosetting resin casing enclosing said section but leaving the eyelet opening exposed, at least one electrolyte-impervious yieldable gas discharge barrier in said casing and in contact with the section to provide for the safe escape of gas from said capacitor, the interior of said capacitor being impregnated with electrolyte said opening in said eyelet being sealed, and an electrically conducting terminal lead being conductively connected to said eyelet.

2. The vented molded tubular electrolytic capacitor deined in claim 1 wherein the electrolyte-impervious yleldable barrier consists of openings in said thermosetting resin casing which are sealed by an elastomer compound.

3. The vented molded tubular electrolytic capacitor defined in claim 2 wherein said elastomer is in the form of a strip of solid material engaged between said capacitor section and said casing covering and sealing said openings.

4. The vented molded tubular electrolytic capacitor defined in claim 1 wherein the electrolyte-impervious yieldable barrier is in the form of an annular opening about the termina1 lead at one end of said capacitor sealed by a washer composed of an elastomer compound.

5. The molded tubular electrolytic capacitor dened in claim 1 wherein one end of said ca-v pacitor section is encased in an end cap of an elastomer material having an opening therein through which said terminal lead projects, an

of said section, an electrically conducting eyeletV connected to the other electrode of said section and having an opening therein for the impregnation of electrolyte, a molded thermosetting resin casing enclosing said section but leaving the 5 eyelet opening exposed, and at least one electrolyte-impervous yeldable gas discharge barrier in said casing and in Contact with the capacitor section to provide for the safe escape of gas from said capacitor.

HAROLD E. BRAFMAN.

REFERENCES CITED Number 6 UNITED STATES PATENTS Name Date Blackburn Jan. 24, 1939 Deutschmann Dec. 26, 1939 Robinson Jan. 20, 1942 Deeley May 12, 1942 Dunleavey Aug. 15, 1944 Menschk Dec. 26, 1950 

1. A VENTED MOLDED TUBULAR ELECTROLYTIC CAPACITOR CONSISTING ESSENTIALLY OF A CONVOLUTELY WOUND ELECTROLYTIC CAPACITOR SECTION, AN ELECTRICALLY CONDUCTING TERMINAL LEAD CONNECTED TO ONE ELECTRODE OF SAID SECTION, AND AN ELECTRICALY CONDUCTING EYELET CONNECTED TO THE OTHER ELECTRODE OF SAID SECTION AND HAVING AN OPENING THEREIN FOR THE IMPREGNATION OF ELECTROLYTE, A MOLDED THERMOSETTING RESIN CASING ENCLOSING SAID SECTION BUT LEAVING THE EYELET OPENING EXPOSED, AT LEAST ONE ELECTROLYTE-IMPERVIOUS YIELDABLE GAS DISCHARGE BARRIER IN SAID CASING AND IN CONTACT WITH THE SECTION TO PROVIDE FOR THE SAFE ESCAPE OF GAS FROM SAID CAPACITOR, THE INTERIOR OF SAID CAPACITOR BEING IMPREGNATED WITH ELECTROLYTE SAID OPENING IN SAID EYELET BEING SEALED, AND AN ELECTRICALLY CONDUCTING TERMINAL LEAD BEING CONDUCTIVELY CONNECTED TO SAID EYELET. 